At the turn of the century, the external combustion engine was replaced for many applications, such as the automobile, with engines of the internal combustion variety. Spurred by the availability of liquid fuels, engine structures such as the Otto (1876) four stroke engine, with fuel-air compression and spark ignition utlimately dominated the automotive and other fields. Diesel (1892) introduced the compression-ignition diesel cycle engine with fuel injection, while Clerk (1878) developed the two-stroke cycle in an effort to improve the weight-to-power ratio of engines and achieve some valve simplification. The former ratio is improved inasmuch as two-stroke cycling doubles the number of power strokes otherwise developed in a four-stroke system. To accommodate for the exhaust stroke otherwise provided in a four cycle architecture, the two-cycle engine generally employs a scavenging exhaust technique. Several scavenging variations have been developed, for example, cross-scavenging including piston carried deflectors, loop scavenging and through or uniflow scavenging. See generally in this regard, "Internal Combustion Engines and Air Pollution" by E. F. Obert, 1973, Harper & Row, Publishers, Inc.
In any of the above-noted internal combustion systems, a variety of accoutrements or peripheral support systems are necessitated. The timed valving and associated camshaft assembly are called for in stroke definition. Pistons reciprocate in conjunction with crankshaft assemblies which, in turn, are lubicated from a reservoir and driven oil pump system circulating lubricating oil. Cooling generally calls for a radiator and associated water pump with cooling jacket structure about the engine cylinders. All of these peripheral components call for continuous maintenance and represent friction factors or drag in weight. The latter aspect impairs attempts to improve output power to weight ratios. Significant efforts have been put forth by investigators to overcome the necessity for many of these peripheral devices. For example, rotary engines such as those developed by Wankel (1970) perform with essentially one moving part, a rotor, and achieve higher power-to-weight ratios but at fuel efficiency losses. Ceramic structures continue to be investigated for the promise of high temperature performance without cooling systems. However, suitable ceramic materials have yet to be identified. The compounding of engines and processes such as free piston systems have been proposed, however, with no particular commercial success, due principally to cost factors.
A prominent cost factor associated with engine structuring resides in a necessary customization of design to a given application. For instance, power requirements from lesser to greater are met by generally unique, custom engine designs with corresponding customization of peripheral support equipment. No effective modularity has been introduced for upscaling or downscaling engine structures to meet different applications.